JPH0729220A - Formation of fine pattern having plural heights - Google Patents

Abstract

PURPOSE:To form a fine pattern having plural heights in a photolithographic process for producing the master of an optical disk. CONSTITUTION:The front side of a substrate 1 with a formed photoresist 2 is irradiated with light from the rear side of the substrate 1 at a larger angle than a critical angle from the substrate 1 to the photoresist 2, the photoresist 2 is exposed with light leaking in the photoresist 2 from the substrate 1 and development is carried out. The objective fine pattern having different heights is formed by varying the incident angle or wavelength of light at the time of exposure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is useful, for example, in manufacturing an optical disk master having a fine pattern.

[0002]

2. Description of the Related Art Generally, a photolithography process is often used as an example of a conventional fine pattern forming method. Here, a method of manufacturing a reproduction-only optical disc master using a photolithography process will be described.

FIG. 5 shows a conventional method for manufacturing a read-only optical disk master. The reproduction-only optical disk master is roughly classified into the following: (a) a step of applying a positive photoresist 20 onto a mirror-polished glass disk substrate 1 by a spin coating method or the like (b) the disk substrate While rotating 1, turn on and off the laser beam focused by the lens according to the recording signal.
It was manufactured by a step of exposing the photoresist 20 by exposing it to F and exposing it to the substrate (c) a step of dissolving the exposed portion 3 by development.

[0004]

Since the storage capacity of the optical disk shown in the conventional example is limited by the beam waist size determined by the recording laser wavelength and the aperture (NA) of the condenser lens, the high density in the surface direction is obtained. There is a limit to conversion.

Current optical discs have reached the limit of densification in the surface direction, but have only binary information in the depth direction depending on the presence or absence of signal pits. Therefore, in order to further increase the recording density, a method of providing information in the depth (height) direction of the signal pits can be considered.

However, it has been difficult to change the depth of the signal pit for recording by the ordinary photolithography process as in the conventional method for manufacturing an optical disk master.

In view of the above-mentioned problems of the prior art, the present invention provides an optical disc master having signal pits having different depths.
It is an object of the present invention to provide a method for forming a fine pattern having different heights.

[0008]

In order to achieve the above object, as a first means of a method for forming a fine pattern, a step of forming a photosensitive material layer on the front surface of a base material, a base material surface for recording light. Is θ and the total reflection angle when light is incident on the photosensitive material from the substrate is θ _c , θ _c <θ <π (r
The process of irradiating the recording light from the back side of the substrate so as to change θ in the range of (ad), and exposing the photosensitive material by the light of the recording light that seeps from the base material to the photosensitive material, except the photosensitive part. A fine pattern having a plurality of heights is formed by a developing process for removing the.

As a second means, the step of forming a photosensitive material layer on the surface of the substrate, the incident angle of the recording light with respect to the surface of the base material is θ, and all of the light is incident on the photosensitive material from the base material. When the reflection angle is θ _c , the wavelength of the recording light is changed at one incident angle within the range of θ _c <θ <π (rad), and the recording light is irradiated from the back side of the substrate. A fine pattern having a plurality of heights is formed by a step of exposing the photosensitive material by light bleeding from the base material to the photosensitive material and a developing step of removing a portion other than the photosensitive portion.

[0010]

According to the above means, the following effects can be obtained.

When incident light is incident from the back side of the front (front) surface of the base material at an angle θ of total reflection, most of the incident light does not pass through the base material and is totally reflected on the base material surface. Is reflected. However, at this time, light that travels in parallel with the surface of the substrate and whose light intensity exponentially decreases in the direction perpendicular to the substrate exudes from the surface of the substrate to the photosensitive material side. This light is called the evanescent wave, and the light emitted from this spot exposes the photosensitive material.

With respect to the exudation depth, the depth at which the light intensity is 1 / e ² with respect to the light intensity at the interface between the substrate and the photosensitive material is d,

[0013]

[Equation 1]

It is expressed by the following equation (Equation 1). In the above equation, λ is the wavelength of the recording light, θ is the angle of incidence on the interface between the substrate and the photosensitive material, and n ₁ and n ₂ are the refractive index of the substrate and the refractive index of the photosensitive material, respectively. .

That is, it can be seen that the seeping depth of the recording light into the photosensitive material can be controlled by changing the incident angle θ or the wavelength of the recording light. As the exuding depth changes, the photosensitive material also changes in depth, so by developing it and removing the unexposed areas, the height can be changed depending on the incident angle or wavelength of light. A pattern can be formed.

For reference, the laser wavelength is set to 457.
9 nm, the substrate refractive index is 2.61, the photoresist refractive index is 1.5, and the backside angle of the substrate is 45 °.
Table 1 shows the critical angle, the incident angle of the substrate surface with respect to the incident angle of the substrate, and the penetration depth into the photoresist.

[0017]

[Table 1]

[0018]

The present invention will be described in detail below with reference to specific examples.

(First Embodiment) FIG. 1 shows a process chart of a first embodiment of the present invention. In FIG. 1, 1 is a base material, 2 is a photoresist, and 3 is an exposed portion. Further, FIG. 2 shows a schematic diagram of the exposure apparatus used in this embodiment. In FIG. 2, 4, 5
Is a mirror, 6 is an Ar laser for recording (λ = 457.9n
m).

First, a case will be described where a pattern having different heights is formed on one side surface of a base material having a triangular prism shape as shown in FIG. The base material is SrTiO ₃ (wavelength 45
A cutout of n ₁ ≈2.61) at 7.9 nm is used.

First, a negative photoresist O is formed on the side surface A.
MR-85 (Tokyo Ohka Kogyo, refractive index ≈1.5) thickness 2
Apply at about 00 nm. In the present invention, a photoresist of the type in which the unexposed portion is removed during development is called a negative type photoresist.

Next, as shown in FIG. 2, laser light is irradiated from the side surface C at an angle at which the incident angle with respect to the side surface A is 24 ° (optical path shown by the solid line in FIG. 2), and the substrate 1 In the z direction. This allows linear exposure in the z direction on the side surface A of the substrate 1. The laser light intensity incident on the substrate is 40 m.
The moving speed of W and the substrate 1 is 10 mm / sec.

Next, the position and angle of the mirror 4 are changed so that the incident angle of the laser beam is 40 °, and the other conditions are the same as the above conditions (the optical path indicated by the broken line in FIG. 2). The photoresist 2 is exposed from the back side of A (see FIG. 1).
(B)).

By developing the base material which has been subjected to the above-mentioned treatment and removing the unexposed portion, groove patterns having different heights as shown in FIG. 1 (c) can be obtained. The obtained groove heights are about 90 nm and about 45 nm when the incident angle is 24 ° and 40 °, respectively. In this embodiment, the groove height is about 0.6 times the bleeding depth, but the height can be changed to some extent by changing the developing conditions.

As described above, according to this embodiment, it is possible to form patterns having different heights on the substrate 1, and it is possible to control the pattern height by changing the incident angle of the recording light. it can.

In the present embodiment, the incident angle was changed only under two conditions, but it is easy to change the incident angle under more conditions, whereby a large number of incident angles can be obtained. It is possible to form patterns having different heights.

In this embodiment, the base material is
Although the slope angle of 45 ° was used, the smaller the slope angle of the back surface of the base material with respect to the front surface of the base material, the smaller the incidence angle of the recording light on the base material has to be made to enter from the direction parallel to the base material. Therefore, it is preferable that the slope angle has an inclination of at least 20 ° or more with respect to the surface of the base material.

Regarding the control of the pattern height, in order to reduce the pattern height, the slope angle should be increased or
A material having a high refractive index may be used as the base material.

As the high refractive index base material, in addition to SrTiO ₃ used in this embodiment, BaTiO ₃ (n ₁ = 2.5) is used.
4), ZnS (n ₁ = 2.46) (n ₁ is the refractive index when the recording light wavelength is 457.9 nm) and the like have the same effect. Conversely, to increase the pattern height,
The slope angle may be reduced or a material having a low refractive index may be used as the base material.

(Second Embodiment) Next, as a second embodiment of the present invention, as a base material, a V-shaped groove having a slope angle of 30 ° is spirally formed on the back surface of the base material with a diamond cutting tool in advance. A case will be described in which a base material is used and a signal pit array having two types of depths is formed on the surface of the base material. The material of the base material was SrTiO ₃ (n ₁ ≈2.61) as in Example 1.
(However, λ = 457.9 nm), ≈3.00 (however, λ = 3
63.8 nm)) is used.

The difference between this embodiment and the first embodiment is that the first embodiment
The incident angle is changed to form different heights in the embodiment, whereas the incident angle is fixed in this embodiment and the height is controlled by changing the wavelength of the recording light.

The present embodiment will be specifically described below. FIG. 3 schematically shows the exposure apparatus used in this embodiment. In FIG. 3, 7 is a dichroic mirror (363.8 nm reflection, 457.9 nm transmission), 8 is A
r laser (wavelength 363.8 nm), 9 is Ar laser (wavelength 457.9 nm), 10 and 11 are objective lenses, 1
Reference numeral 4 is a control laser, 15 is a focus and tracking control system block, and 16 and 17 are EO modulators corresponding to respective wavelengths.

First, the negative photoresist 2 is applied on the surface of the substrate 1 to a thickness of about 200 nm.

Next, while rotating the substrate 1, two kinds of laser light 8 and 9 are emitted by the EO modulators 16 and 17, respectively.
It is turned off N, narrowed down with the objective lens 10, and the front surface of the base material is irradiated from the back surface side of the base material. The beam incident positions on the dichroic mirror 7 are adjusted so that the focus positions of the two types of beams are aligned on the circumference in the radial direction of the substrate 1.

The recording conditions are as follows: the incident angle of the recording light on the substrate is 47 °, and the incident beam intensities of the beams with wavelengths of 363.8 nm and 457.9 nm are 10 m, respectively.
W, 20 mW, and linear velocity of 10 m / sec.

Further, it is utilized that the laser light from the control laser 14 is condensed by the objective lens 11 on the slope mountain portion or the valley portion on the back surface of the substrate 1 and the intensity distribution of the reflected light is asymmetric. This enables tracking control and
Focus control is performed by the control optical system so that the recording light is focused on the boundary between the substrate 1 and the photoresist 2.

By developing the exposed base material and removing the unexposed portion, the pit height becomes a wavelength of 363.8 nm.
40nm, 457.9nm for recording with beam
The beam of 2 gives a signal pattern having two heights of about 110 nm. For reference, the values of the bleeding depth to the photoresist side (depth at which the intensity is 1 / e ^{2 of the} boundary) at each wavelength are shown in (Table 2) and (Table 3).

Here, (Table 2) shows that the laser wavelength is 36
The incident angle of the substrate surface with respect to the critical angle and the incident angle of the substrate when the refractive index of the substrate is 3.8 nm, the refractive index of the substrate is 3.00, the refractive index of the photoresist is 1.5, and the slope angle of the back surface of the substrate is 30 °. ,
And the depth of seeping into the photoresist.

Further, (Table 3) shows a laser wavelength of 457.9.
nm, the substrate refractive index is 2.61, the photoresist refractive index is 1.5, and the backside angle of the substrate is 30 °, the critical angle, the substrate incident angle with respect to the substrate incident angle, and This shows the depth of seeping into the photoresist.

[0040]

[Table 2]

[0041]

[Table 3]

As described above, according to this embodiment, it is possible to form patterns having different heights on the base material, and the pattern height can be controlled by changing the wavelength of the recording light.

In this embodiment, the base material in which the V-shaped groove is formed in a spiral shape is used, but there is essentially no change in the concentric V-shaped groove array, and the same effect can be obtained.

If the recording light is incident on the interface between the substrate surface and the photoresist at an angle at which the recording light is totally reflected at the interface between the substrate surface and the photoresist instead of the symmetrical V-groove shape as in this embodiment, an asymmetric wedge shape is obtained. Alternatively, a similar effect can be obtained with a groove having a rectangular shape, a trapezoidal shape, a semicircular shape, or the like.

(Third Embodiment) Next, as a third embodiment of the present invention, a circular base material having a V-shaped groove with a slope angle of 30 ° on the back surface is used as the base material as in the second embodiment. A case will be described in which a signal pit row whose height continuously changes is formed on the material surface. The material of the base material is S as in the first and second embodiments.
rTiO ₃ is used.

FIG. 4 schematically shows the exposure apparatus used in this embodiment. 4, 18 is a wavelength tunable organic dye laser (7-hydroxycoumarin: wavelength 450 to 470 nm), and the objective lenses 10 and 11 which are independent in FIG. The other parts are the same as those shown in FIG.

The present embodiment will be specifically described below. First, the negative photoresist 2 is applied to the surface of the base material 1 to a thickness of about 200 nm.

Next, while rotating the substrate 1, the wavelength of the laser light is modulated in accordance with the signal to be recorded, and EO
The recording pulse length is also modulated by the modulator 18, and the recording pulse length is made incident from the rear surface side of the base material so that the angle is satisfied from the outer peripheral portion of the shared objective lens 19.

The recording conditions are as follows: the angle of incidence of the recording light on the base material is 45 °, the wavelength variation width is 450 nm to 470 nm, the incident beam intensity on the objective lens is 20 mW, and the linear velocity is 1.
It is 0 m / sec.

Further, the laser light from the control laser 14 passes through the center of the common objective lens 19, and the laser light from the second embodiment is used.
Tracking and focus control are performed in the same manner as the method shown in FIG.

By developing the exposed substrate and removing the unexposed portion, the pit height is about 160 nm to 17 nm.
It is possible to obtain a signal pit train that changes in the range of 0 nm.

Further, since the recording beam and the control beam are condensed by one objective lens, there is an advantage that the optical system can be easily realized as compared with the second embodiment. However, since the aperture of the lens cannot be fully utilized, the recording beam is not sufficiently condensed. In practice, it can be said that the condensing optical system to be used should be decided after considering the required recording density.

As described above, according to the present embodiment, it is possible to form the signal pit train whose height continuously changes on the base material.

The present invention has been described above in detail based on the first to third embodiments. In order to form patterns having different heights, the incident angle of the recording beam was changed in the first embodiment and the wavelength of the recording beam was changed in the second and third embodiments. The same effect can be obtained as in the first embodiment, and the method of changing the wavelength in the first embodiment and the method of changing the incident angle in the second and third embodiments may be used.

[0055]

According to the present invention, it becomes possible to form a fine pattern having a plurality of heights on the surface of a substrate, and thus it is possible to perform recording at a higher density than in the past.

[Brief description of drawings]

FIG. 1 is a process chart showing an embodiment of the present invention.

FIG. 2 is a schematic diagram of an exposure apparatus used in the example.

FIG. 3 is a schematic diagram of an exposure apparatus used in another embodiment of the present invention.

FIG. 4 is a schematic diagram of an exposure apparatus used in still another embodiment of the present invention.

FIG. 5 is a process diagram showing a conventional pattern forming method.

[Explanation of symbols]

 1 Base Material 2 Negative Photoresist 3 Exposure Section 4 Mirror 5 Mirror 6 Ar Laser 7 Dichroic Mirror 8 Ar Laser (Wavelength 363.8 nm) 9 Ar Laser (Wavelength 457.9 nm) 10 Objective Lens 11 Objective Lens 12 λ / 4 Wavelength Plate 13 Polarizing Beam Splitter 14 Control Laser 15 Control System Block 16 EO Modulator 17 EO Modulator 18 Wavelength Tunable Laser 19 Common Objective Lens 20 Positive Photoresist

Claims (10)

[Claims] 1. A method of forming a fine pattern having a plurality of heights, comprising: a step of forming a photosensitive material layer on the front surface of a substrate; an incident angle of recording light with respect to the substrate surface being θ; when the critical angle of total reflection when incident light to the photosensitive material was θ _c, θ _c <θ <to vary the theta range of π (rad),
Multiple heights consisting of the process of irradiating the recording light from the back side of the substrate and exposing the photosensitive substance by the light of the recording light that leaks from the base material to the photosensitive substance, and the developing process to remove the non-photosensitive portion. A method for forming a fine pattern having: 2. A method of forming a fine pattern having a plurality of heights, the method comprising: forming a photosensitive material layer on a substrate surface; an incident angle of recording light with respect to the substrate surface being θ; When the critical angle of total reflection when light is incident on a substance is θ _c , the wavelength of the recording light is changed at one incident angle within the range of θ _c <θ <π (rad), and the backside of the substrate is changed. Fine light with multiple heights, consisting of the steps of irradiating recording light from the surface and exposing the photosensitive material by the light of the recording light that exudes from the base material to the photosensitive material, and the developing step of removing the areas other than the photosensitive area. Pattern formation method. 3. The base material, wherein the back surface of the base material has a substantially inclined surface shape with respect to the front surface of the base material is used.
A method for forming a fine pattern having a plurality of heights described. 4. The method for forming a fine pattern having a plurality of heights according to claim 1 or 2, wherein a base material having a substantially wedge-shaped groove array on the back surface is used as the base material. 5. The method for forming a fine pattern having a plurality of heights according to claim 4, wherein the substantially wedge-shaped groove is formed in a concentric shape or a spiral shape. 6. The substrate according to claim 3, wherein the angle of the substantially inclined surface of the back surface of the base material is 20 ° or more and less than 90 ° with respect to the front surface of the base material.
Alternatively, the method for forming a fine pattern having a plurality of heights according to 4 above. 7. The method for forming a fine pattern having a plurality of heights according to claim 1, wherein a negative photoresist is used as the photosensitive material. 8. The method for forming a fine pattern having a plurality of heights according to claim 1, wherein the recording light is condensed by a lens on a substantially boundary surface between the substrate and the photosensitive material. 9. The method for forming a fine pattern having a plurality of heights according to claim 4, wherein the tracking control is performed by the reflected light from the substantially sloped groove when the recording light is irradiated. 10. The method for forming a fine pattern having a plurality of heights according to claim 4, wherein the focus control is performed so that the recording light is focused on a substantially boundary surface between the substrate and the photosensitive material when the recording light is irradiated. .